In some societies, it is common for men to think of wives and daughters as both assets and liabilities. So long as they are obedient to their fathers and husbands, they are a source of pride. But if they disobey and show independence, they become a source of shame and may even be murdered to protect the family's "honor."

Here are five things to know about "honor killings" and why they are so hard to stop.

How frequent are honor crimes?

According to UN statistics available, some 5,000 honor killings a year are reported worldwide. But many experts believe the real number is much higher because many honor crimes are often hidden from the police.

The hiding of honor crimes is possible because they often take place within a family. Leading members, including females, decide that the woman or girl who has compromised the family's honor must be put to death. The crime is kept secret through a code of silence.

Jacqueline Thibault, whose Swiss-based association Surgir protects potential victims of honor killings in the Middle East, says murders are often reported as suicides. In some cases, there is no "need" for a murder because the family pressure is so great that the victim commits suicide herself.

Are honor crimes unique to the Muslim world?

No, honor crimes are found in many parts of the globe and are not tied to any single religion. Countries where they take place are as diverse as Brazil and India, Pakistan and Albania. However, they occur with the greatest frequency in the Middle East and South Asia and only sparingly in South America and Central Asia, as well as among some immigrant populations in Europe.

"Honor crimes tend to happen in places where there are inflexible and discriminatory attitudes about women's roles, especially around their sexuality, and these are often applicable to women but not exclusively so, because sometimes men are targeted for honor crimes as well," says Rothna Begum, Middle East and North Africa researcher for Human Rights Watch (HRW).

"Women or couples seen as having brought dishonor on the community or family face violence, which is then held out as a chilling example for others."

Experts say that honor killings are linked to patriarchal societies and the earliest historical evidence of them dates back to Babylon. They arise from the notion that women are the vessels of a family's honor and are closely tied to values placed on marriage with virgin brides. Under this concept of honor, a family's inability to guarantee a daughter's virginity prior to marriage is a cause for shame and for ostracism by neighbors.

But there are also economic factors at work.

Thibault says that in societies that practice arranged marriages, unions are as much about ensuring the common interests of the two families as those of the betrothed.

"These are marriages between families much more than between a man and a woman and marriages between families are to obtain a better economic situation, to get more farmland, to have a better social standing," says Thibault. "If the marriage is threatened or broken off, the family no longer attains what it hoped for in terms of better social or economic status."

Why are laws alone insufficient to protect victims?

Honor killings are illegal around the world, but many legal systems are lenient with those who commit them because the perpetrators are seen by the society as defending traditional values.

The leniency shows up in legal loopholes that allow killers to go free. One common loophole is a provision that allows the victim's closet kin to forgive the killer.

"Because the victim is killed by the family themselves, the family is able to forgive the family member who killed the wife, or daughter, or sister," says Begum. "So you are in a situation where the murderer gets away with it."

Some murders occur even after the girl has left her family, but the loopholes still apply. The killer can ask forgiveness from the husband's family and hope social pressure will ensure he gets it. He can also hope the other family will accept monetary compensation, or "blood money," for the crime so that he is spared punishment.

How do potential victims of honor killings protect themselves?

Because victims are targeted by their own families, protection is very difficult. Just how difficult can be measured by the fact that in some countries, including Jordan and Afghanistan, potential victims sometimes seek refuge in prisons where, despite being incarcerated, they are at least beyond their families' reach.

However, Thibault notes that women cannot simply ask to be put in jail. The legal system requires they be guilty of a crime, so the girls first confess to a misdemeanor they have not committed.

Once in prison, the girls may hope that over time their families may agree to take them back or not to track them down after they are released. But Thibault, whose organization tries to mediate family reunions in Jordan, says there is never any certainty of forgiveness.

"Our social workers mediate with the families to see if the families will accept them back despite everything," she says. "In some cases, very few, the families accept, but one can never be sure that it will last and that the family won't kill her two months later. Each case has to be followed very closely."

Are honor crimes on their way out?

Honor crimes have existed in societies where they no longer exist today, including in remote rural areas of Greece and southern Italy as recently as the early decades of the last century. But experts say they are hard to eradicate unless laws against them are strictly enforced.

"It really comes down to how the laws are being implemented and changed," says Begum. "In countries where they continue to have mitigating circumstances or offenses that allow for the offenders to be pardoned, there is no deterrent and it sends a message to society that it is OK to kill the women of their families if they breach their honor."

In the most recent case in Pakistan, where Farzana Parveen was bludgeoned to death on May 26 by members of her family for marrying a man of her own choice, her husband, Muhammad Iqbal, has himself told reporters that he strangled his first wife so he could marry Farzana. The fact that he escaped punishment for that crime only to lose his next wife to an honor killing underlines the revolving-door nature of laws that are not enforced.

Khawar Mumtaz, chairwoman of Pakistan's National Commission on the Status of Women, says her commission is aware that the loopholes in the law are abused and wants them closed.

"There is a loophole in our law under which the affected families forgive the killers [through a mutual compromise]," Mumtaz says. "But there is also another section 311 in the Penal Code under which such people could be punished [but which] is usually not applied in the first investigation report. We are trying to apply this so that the family's pardon does not help [the accused]."